Extensive resources are being committed to improve global childhood vaccination coverage, but the response to standard vaccination is often diminished in children from developing nations. The ineffectiveness of vaccination programs in developing communities has been blamed on cold chain lapses and lack of supportable infrastructure, but chronic infections also play a significant role. Multiple maternal parasitic infections affect the unborn infant and are potentially important vaccine response modifiers, but have not been well studied. Increasing evidence suggests that chronic parasitic infections in pregnant women, such as schistosomiasis, filariasis, intestinal helminths, and malaria, can suppress fetal and infant immune responses to subsequent infections and vaccinations. The mechanisms of parasite effects on immune responses are not well understood, although the lack of appropriate vaccine response in infants of parasite-infected mothers appears to be due to dysregulation of maternal immunity, with resultant impaired fetal immunity. The central hypothesis to be tested is that treatment of maternal and infant parasitic infections will enhance infant responses to vaccination. We propose a prospective study of pregnant Kenyan woman and their offspring to evaluate the effects of parasitic infections and prompt anti-parasitic treatment on infant vaccine responses to polio, Haemophilus influenzae, and diphtheria. We propose the following specific aims: 1) to determine the individual and combined influence of maternal parasitic infections on infant vaccine responses, and 2) to measure the impact of maternal and infant anti-parasitic treatment on infant vaccine responses. The long term goals of this project are to determine the value of specific antenatal and postnatal parasitic treatments and to develop novel approaches to optimizing vaccine program effectiveness.